I would also recommend a subscription to
Base Ball: A Journal of the Early Game. Two issues each year, focusing on pre-1920 baseball with a significant emphasis on the 19th-century game. John Thorn was the first editor, and now Peter Morris has taken over. A wonderful range of articles from many of the most prominent baseball researchers. I have really enjoyed my subscription, which comes with a great electronic access page that includes back issues.
http://www.mcfarlandpub.com/baseball.html
Finally, how about a SABR membership?
Best,
Charles